1. Field of the Invention
The present disclosure relates to semiconductor lasers including transparent output windows and, more particularly, to methods for fabrication of such lasers and to the reliability of such lasers.
2. Technical Background
The present inventors have recognized that the lifetime of edge-emitting semiconductor lasers is often shortened by failures caused by catastrophic optical mirror damage (COMD) at and near the output facets. The mechanism of COMD involves a few related physical processes, occurring at and near a laser output facet, including absorption of light, oxidation of semiconductor material, electrical current on the facet surface and non-radiation recombination of free carriers at defect centers. Theoretically, these physical processes can interact with one another and cause rapid temperature rise, which in turn accelerates the above-noted physical processes, increasing the likelihood of laser facet melting, defect growth, and laser failure.
Facet passivation is often employed to reduce the aforementioned COMD failure rate. However, some passivation techniques can be relatively low throughput processes and often require sophisticated equipment, and are often not suitable for mass production. An example is the E-2 passivation process, where laser bars are cleaved in ultra-high vacuum and are immediately treated with protective layers to prevent oxidation of semiconductor materials at the facets. Alternative passivation processes, such as processes where laser bars with transparent output windows are cleaved in air and there is no in-situ thin silicon coating on the cleaved facets, are more suitable for mass production but have not been recognized to be as effective as more cumbersome passivation processes, such as the E-2 process.